Wind tunnel helps shape cars and boats


What does it feel like to walk through a hurricane? What submarine design produces the least drag? Which sail catches the wind best? How much steel does a building need to stand up to strong gusts?

Since 1949 scientists at the University of Maryland have been using the Glenn L. Martin Wind Tunnel in College Park to answer those questions and more.

Shaped like a squared-off doughnut, the tunnel stirs up the air with a 20,000-horsepower fan with blades 20 feet in diameter that can generate wind speeds up to 230 mph.

Ford Motor Co. uses the tunnel to help make its automobiles more aerodynamic and pays fees to the college, which help keep the tunnel self-supporting. To test a new design, Ford builds a scale model out of clay and engineers place it in the tunnel. Then they turn on the wind - usually at 120 miles per hour.

"We can run [auto tests] anywhere from 100 to 140, and we can calculate what the force will be at any speed," said Jewel Barlow, director of the tunnel since 1977 and a professor of aerospace engineering.

Initially the shape of a car is based solely on what the designers deem stylish, but the clay enables quick and easy changes to be made. And reducing drag can have a significant effect on fuel economy, Barlow says.

NASCAR racers also make their way to the tunnel for tweaking to get the edge on competition, but Formula One cars have to go elsewhere. They're so low that that ground-air interaction has a significant effect on their performance. To properly simulate this, a wind tunnel with a moving floor must be used.

The Martin tunnel can also test marine designs because air and water fluid dynamics are the same up to high speeds. Many boat hulls cannot be tested because there's no way to simulate the water's interaction with the surface of the boat at the waterline, but submarine models work fine because they are submerged.

Not all boat tests are about water. The tunnel has also recently been host to Quantum Sails and the Oracle BMW Racing teams, refining their sail designs.

Over the decades, officials say, the tunnel has conducted at least 1,800 experiments on objects as varied as aircraft thrust reversers and garbage cans. But its popularity soars around this time of year, as the hurricane season begins.

That's when the news media start asking for a chance to put a reporter or photographer in the tunnel. Officials say they can't interrupt long-scheduled experiments, but they did open the tunnel to reporters for a day late last month to give visitors a shot at standing up to a hurricane.

As they engineers cranked the wind up to 115 mph - the speed of Category 3 hurricane and the engineers' limit for humans - a climbing harness secured visitors to the floor to keep them from falling or being blown away.

The tunnel itself is a loop. Twenty feet wide where the fan is turning, the tube narrows to about 8 feet high and 11 feet wide in the test area, which increases the speed of the wind.

A reporter who was tested by the tunnel felt pressure building over the front of his body as the wind speed increased, with his clothing eventually flapping so hard that his arms and legs became almost numb, and it became difficult to breathe.

Visitors aside, the wind tunnel does some testing related to hurricanes. Barlow says about 10 percent of its experiments involve the survivability of buildings in high winds.

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